[求助] GWD1-Q32-已爬文,但並沒有解答我的疑惑!

GWD1-Q32: 

To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.

1. have to know a great deal more than now about the social and economic
2. have to know a great deal more than they do now about the social and economical
3. would have to know a great deal more than they do now about the social and economical
4. would have to know a great deal more than they do now about the social and economic
5. would have to know a great deal more than now about the social and economical

BCE可以淘汰。社會的跟經濟的正確用法應該是social and economic ….

但是我比較有疑惑的是在面對A跟D兩個答案時,在語態上為什麼不是選A而是選D? have to 跟 would have to 語氣上,後者有"應該必須..."的意思,可是,A的選項在文法判斷上並沒有明顯的問題呀?

煩請各位賜教.謝謝~~

同意楼上的意见.A的问题在于more than now比较对象不清晰，是错误的。显然D中more than they do now 指代清楚。

那么单纯考虑have to 和would have to，他们在意义表达上有什么区别呢~~请nn指点~~

嗯，记住“社会和经济的“是social and economic”。。。。。。。

thanks